The present invention relates to a series hybrid traction assembly for a motor vehicle, said assembly comprising an electric generator set, at least one dual traction set comprising two electric motors driving respective second shafts aligned with each other and coupled respectively to a left wheel and a right wheel of the vehicle, and at least one static converter connected in series between the generator set and the tandem traction set.
The invention also relates to a series hybrid vehicle comprising such a traction assembly.
In most cases, the drive wheels driven by a dual electric traction set are coupled to the second shafts of the set by means of articulated transmission shafts providing sufficient angular play for the suspension clearance, and for the angle of lock of the wheels if they are leading wheels. It is important that these transmission shafts have the longest length possible, in order to reduce the maximum angle of the articulation joints, i.e. it is desirable for the traction set outputs to be as close as possible to each other.
U.S. Pat. No. 5,172,784 discloses a motor vehicle having a drive system of the kind indicated hereinabove, wherein the dual traction set comprises two coaxial electric motors, having a common stator and two rotors aligned with each other which each drive a rear wheel via a corresponding shaft. The generator set, formed in this case by an external combustion engine associated with a linear generator, is placed in the front of the vehicle. It supplies the electric motors through a converter assembly placed partly in the middle and partly at the rear of the vehicle. An auxiliary battery capable of providing reserve drive energy is placed in front of the rear axle.
The traction set provided in the aforementioned Patent unfortunately requires too much space to be used in a small vehicle, in particular because its axial length is equal to the sum of the lengths of the two motors, which excessively reduces the length of the transmission shafts. Further, since the motors rotate at the same speed as the wheels, they have to have a relatively large diameter to provide sufficient torque.
It is possible to overcome these drawbacks by using reducing gears. Each drive wheel is then driven by a back-geared motor comprising an electric motor and an appropriate reducing gear. U.S. Pat. No. 4,351,405 proposes simply to omit the transmission shafts and replace each of them with a reducing gear, but this solution is unsatisfactory from the point of view of the suspension. On the other hand, since it concerns a parallel hybrid traction vehicle, the heat engine is placed close to the other axle, which it drives directly.
A better solution is disclosed in French Patent 328 430, which concerns an electric car with a rigid driving axle. A reducing gear is associated with each wheel of this axle and it is connected, by a long articulated transverse shaft, to the corresponding motor which is placed close to the other wheel, i.e. the two shafts pass through almost the entire vehicle, respectively in front of and behind the rigid axle. This arrangement remains nonetheless bulky and the reducing gears are not suspended.
In the electric vehicle forming the subject of Patent Application EP 0 544 597, the traction set placed in the middle of the width of the vehicle comprises two motors arranged in parallel one in front of the other, and two reducing gears arranged respectively to the left and right. The axial length of this set is thus quite large, which restricts that of the transmission shafts.
Patent application EP 0 249 807 discloses a dual traction set with reducing gears wherein the two back-geared motors are arranged symmetrically to each other with respect to the median plane, their reducing gears being juxtaposed along this plane within a common casing. The two electric motors, which are of the external rotor type, are arranged along a same axis as the reducing gear first shafts, each motor being on the same side of the median plane as the wheel which it drives. The axial length of the traction set, in the transverse direction of the vehicle, is equal to the sum of the axial lengths of the two reducing gears and the two electric motors. The traction set consequently requires a relatively large space, on both sides of the median plane which is usually in the middle of the width of the vehicle, which may prevent other relatively thick elements being mounted at the side of the traction set. In particular, in a hybrid traction vehicle, it becomes difficult to install the heat engine in the same compartment of the body of the vehicle.
Patent Application DE 24 04 427 discloses, for a purely electric lifting truck, a similar traction set, but wherein the two motors are on the same side of a common reducing gear casing, in order to facilitate their accessibility for maintenance. There is no generator set in this vehicle.